The present invention relates generally to gas turbine engine exhaust nozzles, and in particular to noise reduction and performance improvements to nozzle arrangements used for gas turbine engines suited to aircraft propulsion.
Gas turbine engines are widely used to power aircraft. As is well known, the engine basically provides propulsive power by generating a high velocity stream of gas which is exhausted rearwards through an exhaust nozzle. A single high velocity gas stream is produced by a turbojet gas turbine engine. More commonly nowadays however two streams, a core exhaust and a bypass exhaust, are generated by a ducted fan gas turbine engine or bypass gas turbine engine.
The high velocity gas stream produced by gas turbine engines generates a significant amount of noise, which is referred to as exhaust or jet noise. This noise is generated due to the high velocity of the exhaust stream, or streams, and the mixing of the streams with the surrounding atmosphere, and in the case of two streams, as the bypass and core streams mix. The degree of noise generated is determined by the velocity of the stream and how the streams mix as they exhaust through the exhaust nozzle.
Increasing environmental concerns require that the noise produced by gas turbine engines, and in particular aircraft gas turbine engines, is reduced and there has been considerable work carried out to reduce the noise produced by the mixing of the high velocity gas stream(s). A large number of various exhaust nozzle designs have been used and proposed to control and modify how the high velocity exhaust gas streams mix. With ducted fan gas turbine engines particular attention has been paid to the core stream and the mixing of the core and bypass exhaust streams. This is because the core stream velocity is considerably greater than the bypass stream and also the surrounding atmosphere and consequently the core exhaust stream generates a significant amount of the exhaust noise. Mixing of the core stream with the bypass stream has also been found to generate a significant proportion of the exhaust noise due to the difference in velocity of the core and bypass streams.
One common current exhaust nozzle design that is widely used is a lobed type nozzle which comprises a convoluted lobed core nozzle as known in the art. However, this adds considerable weight, drag, and cost to the installation and nowadays short bypass nozzles are favoured with which the lobed type core nozzles are less effective and are also more detrimental to the engine performance than when used on a long cowl arrangement.
An alternative nozzle design that is directed to reducing exhaust noise is proposed and described in GB 2,289,921. In this design, a number of circumferentially spaced notches, of various specified configurations, sizes, spacing and shapes, are provided in the downstream periphery of a generally circular core exhaust nozzle. Such a nozzle design is considerably simpler to manufacture than the conventional lobed designs. This prior proposal describes that the notches generate vortices in the exhaust streams. These vortices enhance and control the mixing of the core and bypass streams which it is claimed reduces the exhaust noise.
Model testing of nozzles similar to those described in GB 2,289,921 has shown that significant noise reduction and suppression can be achieved. However the parameters and details of the design proposed in GB 2,289,921 are not optimal and there is a continual desire to improve the nozzle design further.
A further design, and that of the present Assignee, is proposed in UK Application GB 0025727.9. This application discloses trapezoidal shaped tabs disposed to the axially rearward exhaust ducts of the bypass and core and which are inclined radially inward to impart vortices to the exhaust streams.
However, the main requirement of reducing exhaust noise is during aircraft take-off and landing. At higher altitudes where the majority of the duration of the flight is, exhaust noise is not a problem. It is therefore not necessary to have noise reduction means operational at higher altitudes especially when one considers the noise reduction means inherently introduces aerodynamic inefficiencies.
It is therefore desirable and is an object of the present invention to provide an improved gas turbine engine exhaust nozzle which is quieter than conventional exhaust nozzles and/or which offers improvements generally.
According to a first aspect of the present invention there is provided a gas turbine engine exhaust nozzle arrangement for the flow of exhaust gases therethrough between an upstream end and a downstream end thereof comprising a nozzle, a downstream portion and a plurality of tabs, each tab extends in a generally axial direction from the downstream portion of the nozzle wherein the nozzle further comprises an actuation mechanism capable of moving the tabs between a first deployed position, in the first position the tabs interact with a gas stream to reduce exhaust noise thereof, and a second non-deployed position, in the second position the tabs are substantially aerodynamically unobtrusive.
Preferably, the plurality of tabs is circumferentially disposed about the nozzle.
Preferably, the actuation mechanism comprises a shape memory material element.
Preferably, the nozzle further comprises a radially inner position and a radially outer part, wherein the tabs are rotatably attached to the nozzle at the radially inner position, the actuation mechanism comprises the shape memory element mounted at a first end to a radially outer part of the nozzle and mounted at a distal end to a radially outer part of the tab, such that in use, the element in a first shape maintains the tab in the second non-deployed position and in a second shape maintains the tab in the first deployed position.
Preferably, the periphery of the nozzle defines a pocket therein and at least a part of the element is generally disposed within the pocket.
Preferably, the tab defines a recess therein and at least a part of the element is generally disposed within the recess.
Alternatively, the element is in the form of a spring.
Preferably, the nozzle arrangement comprises a resilient member having a first end and a distal end, the resilient member is attached at the first end to the tab and at the distal end to the nozzle and is arranged to provide a returning force to the tab.
Preferably, the nozzle defines an orifice and a passage, the orifice is exposed to a gas stream and the passage extends from the orifice to the pocket and thereby provides a conduit for transmitting the thermal flux of the gas stream to the actuation mechanism.
Alternatively, the tab comprises shape memory material and the tab further comprises a flexural element, the flexural element, in use, is arranged to provide a returning force to the tab.
Preferably, the tab defines an orifice, the orifice exposed to a gas stream, and a passage, the passage extending from the orifice, to the shape memory material and thereby provides a conduit for rapidly transmitting changes in the thermal flux of the gas stream to and throughout the memory shape material element.
Preferably, the actuation mechanism is actuated in a response to an applied field and the field is a temperature flux. Alternatively, the field is an electric current.
Preferably, the temperature flux is provided by the gas stream and the gas stream is any one chosen from the group comprising an ambient gas flow, a bypass flow, a core flow.
Preferably, the shape memory material element comprises any one of a group comprising Titanium, Manganese, Iron, Aluminium, Silicon, Nickel, Copper, Zinc, Silver, Cadmium, Indium, Tin, Lead, Thallium, Platinum.
Alternatively, the shape memory material element comprises an electrostrictive material and the actuation mechanism further comprises an electrical circuit, the electrical circuit comprising control apparatus, an electric generating means and electrical contact means, the electrical contact means arranged to deliver, in use, an electrical signal, generated by the electrical generating means, through the electrostrictive material, the control apparatus operable to control the electrical signal. Alternatively, the control apparatus is operated to deliver the electrical signal to the electrostrictive material, thereby actuating the electrostrictive material, the tab is moved from a second non-deployed position and a first deployed position and when the control means is operated so as not to deliver the electrical signal the electrostrictive material moves the tab between the first deployed position and the second non-deployed position.
Preferably, when the control apparatus is operated to deliver the electrical signal to the electrostrictive material, thereby actuating the electrostrictive material, the tab is moved between a first deployed position and a second non-deployed position and when the control means is operated so as not to deliver the electrical signal the electrostrictive material the tab is moved from the second non-deployed position and the first deployed position. Furthermore, the control apparatus, operable to control the electrical signal, is operated in response to the altitude of an associated aircraft.
Preferably, the electrostrictive material element comprises any one of a group comprising Lead Zirconate Titanate, Lead Magnesium Niobate and Strontium Titanate.
Alternatively, the electrostrictive material element comprises any one of a polymer group including polyvinylidene fluoride.
Preferably, the downstream portion of the nozzle comprises a downstream periphery, the plurality of circumferentially disposed tabs extend in a generally downstream direction from the downstream periphery.
Preferably, the downstream portion of the nozzle defines a plurality of circumferentially disposed recesses, each recess receiving a tab and when the tab is in a second non-deployed position it substantially occupies a recess.
Alternatively, the tabs comprise a thermal barrier coating disposed to a surface thereof.
Alternatively, the nozzle comprises a thermal barrier coating disposed to a surface thereof.
Preferably, the tabs circumferentially taper in the downstream direction and the tabs are radially inwardly angled at an angle of up to 20xc2x0 relative to the nozzle wall.
Alternatively, the tabs are radially outwardly angled at an angle of up to 20xc2x0 relative to the nozzle wall.
Furthermore, the tabs are circumferentially alternately radially inwardly angled at an angle of up to 20xc2x0 relative to the nozzle wall and radially outwardly angled at an angle of up to 20xc2x0 relative to the nozzle wall.
Preferably, the tabs are of a substantially trapezoidal shape but alternatively, the general shape of the tabs is any one of the groups comprising rectangular, square and triangular shape.
Preferably, the tabs are circumferentially disposed about the periphery of the nozzle wall to define substantially trapezoidal shaped notches between adjacent tabs. Alternatively, the tabs are circumferentially disposed about the periphery of the nozzle wall to define substantially V-shaped notches between adjacent tabs.
Alternatively, the edges of the tabs are curved.
Preferably, the nozzle tabs are radially inwardly angled at an angle of up to 10xc2x0 relative to the nozzle wall.
Alternatively, the tabs extend in circumferentially alternating radially inward and outward directions for mixing the exhaust gas streams.
Alternatively, the actuation mechanism comprises the shape memory element spanning between each circumferentially adjacent deployable tab, the shape memory element having a first length and a second length, so that in use, when the shape memory element is in its first shape the deployable tabs are in the first deployed position and when the shape memory element is in its second shape the deplorable tabs are in the second non-deployed position.
Preferably, the first length of the shape memory element is longer than the second length, so that in use and in the first deployed position the deployable tabs are angled radially outwardly.
Preferably, the first length of the shape memory element is shorter than the second length, so that in use and in the first deployed position the deployable tabs are angled radially inwardly.
Alternatively, in use as a noise reduction means, alternate tabs are rigidly fixed at a radially inward angle and deployable tabs are operable to move between a first deployed position at a radially outward angle, where the deployable tabs interact with a gas stream to reduce exhaust noise thereof, and a second non-deployed position, where the deployable tabs are substantially circumferentially aligned with the alternate tabs.
Alternatively, in use as a noise reduction means, alternate tabs are rigidly fixed at a second non-deployed position and deployable tabs are operable to move between a first deployed position at a radially inward angle, where the deployable tabs interact with a gas stream to reduce exhaust noise thereof, and a second non-deployed position, where the deployable tabs are substantially circumferentially aligned with the alternate tabs.
Preferably, the downstream periphery comprises straight edges, each straight edge having a tab disposed thereto.
Preferably, the actuation mechanism further comprises an end stop, the end stop is configured to provide a positive locator for the tab in either its deployed or non-deployed positions.
Preferably, the exhaust nozzle is a core engine nozzle but alternatively the exhaust nozzle is a bypass exhaust nozzle and the arrangement may comprise a core exhaust nozzle and a bypass exhaust nozzle.
Alternatively, a ducted fan gas turbine engine exhaust nozzle arrangement comprises an outer bypass exhaust nozzle as described in the preceding paragraphs and comprises an inner core exhaust nozzle of a lobed mixer type.
Preferably, the ducted fan gas turbine engine exhaust nozzle arrangement comprises the downstream end of the bypass nozzle being further downstream than the downstream periphery of the core exhaust nozzle. Alternatively, the downstream end of the bypass nozzle is upstream of the downstream periphery of the core exhaust nozzle.
Preferably, the engine exhaust nozzle arrangement is for exhaust noise attenuation.
Preferably, the tabs extend generally in a downstream direction but alternatively the tabs extend generally in an upstream direction.
According to a second aspect of the present invention there is provided a method of operating an aircraft having a gas turbine engine comprising an exhaust nozzle arrangement as claimed in any preceding claim wherein the method comprises the steps of: deploying noise reduction means prior to take-off; not deploying noise reduction means above a predetermined aircraft altitude and; deploying the noise reduction means below the predetermined aircraft altitude.